1. Field of the Invention
The present invention relates to a drive device of a color light emitting diode (LED) used in a display apparatus, and more particularly, to a drive device of a color LED backlight which is capable of precisely adjusting the forward voltages of color LED arrays for each channel to provide optimal forward voltages to the respective color LED arrays, independently setting the number of LEDs for each color LED array, and reducing ripple of the forward voltages by voltage regulation.
2. Description of the Related Art
In general, at least two hundred eighty million display products are being demanded each year in a mobile display market including mobile phones, MP3 players, personal media players (PMP), automotive navigators, mobile or vehicle DVD/AV systems, and laptop computers. Most of the mobile display market is occupied by a thin film transistor-liquid crystal display (TFT-LCD) technology. Competition among enterprises for improvement of price and performance of the TFT-LCD is becoming severe.
Since the TFT is not self-luminous, the TFT LCD requires an additional light emitting element such as a backlight unit (BLU). The BLU can be embodied by various technologies. Most of LCD-BLUs which are commercially available use a cold cathode fluorescent lamp (CCFL). The CCFL has advantages such as high brightness, low manufacturing cost, a simple driving circuit and a thin tube shape. However, since the CCFL is weak against external impact, a mobile TFT-LCD having a size of about 5 inches or less uses a white LED.
FIG. 1 is a block diagram showing the configuration of a conventional drive device of a white LED backlight.
The conventional drive device 10 of the white LED backlight shown in FIG. 1 drives the white LED backlight 20 and includes an I/O interface 11 for inputting/outputting a signal, a control unit 12 for controlling a driving voltage and driving current according to a brightness control signal output from the I/O interface 11, a DC/DC converter 13 for converting the battery voltage Vbat of about 2.8 V into a forward voltage Vf of about 8 V and supplying the forward voltage Vf to the white LED backlight 20 by the driving voltage control of the control unit 12, and a current source 14 for adjusting the amount of driving current Id which flows in the white LED backlight 20 by the driving current control of the control unit 12.
Each LED of the white LED backlight 20 consumes driving current of about 10 mA and a driving voltage of about 1.8 to 3 V.
The conventional drive device of the white LED backlight properly adjusts the driving current amount of the white LED using a method for controlling the current amount of the white LED. More particularly, the control unit 12 can provide a control signal to the current source 14 to adjust brightness in a burst mode.
However, in the conventional drive device of the white LED backlight, ripple is generated in an output voltage of the DC/DC converter. Thus, a ripple phenomenon occurs in the forward voltage Vf. In addition, a boost-up voltage of the DC/DC converter cannot be easily changed.
When a color LED is used instead of the white LED, the number of the color LEDs is restricted by the forward voltage Vf and the forward voltage Vf of each color LED cannot be precisely adjusted.
In the CCFL or the white LED, since color reproducibility falls to about 70 to 80% of the NTSC standard, it is impossible to accomplish accurate color reproduction. In order to solve such a problem, research for implementing color reproducibility of approximately at least 90% using a color light source is actively ongoing. Now, color LEDs (RGB LEDs) are beginning to be commercialized in a liquid crystal display-high definition television (LCD-HDTV) market and an expert LCD monitor market and an application thereof is gradually expanded as a technology develops and production amount increases.
However, in the conventional drive device of the white LED backlight, due to LED characteristics, the color LEDs (RGB LEDs) are different in a driving voltage, that is, the level of a forward voltage Vf, and optical output efficiency. Accordingly, a function for adjusting the forward voltage Vf is required. When the LEDs are connected in series, the number of the LEDs varies or a difference between the forward voltages Vf increases.
In addition, in a mobile device, the DC/DC boost-up converter which generates the forward voltage for driving the LED is used. However, since the DC/DC converter generates the ripple, the forward voltage Vf becomes unstable.